1. Field of the Invention
The invention pertains to rotary joints for connecting the interior of rotary heat exchangers with a stationary fluid supply or exhaust system. Rotary joints are commonly employed with steam heated dryer drums and cooling calendar rolls utilized in paper making apparatus.
2. Description of the Related Art
Rotary joints for supplying fluid medium to rotary heat exchanger drums or calendar rolls used in paper mills are subjected to high radial impact forces when the paper web being treated by the heat exchangers breaks and the web may unevenly wrap around the rolls forming a "cam" effect which separates the rolls and then permits the rolls to clash together. Such an event produces high radial impact forces on the rotary joints associated with such drums or rolls breaking the seals in the rotary joints causing the joint bearings to flood with coolant, and the bearings may be destroyed as lubricant is lost. Paper making mills run for extended durations as measured in months between shutdown, and it is very important that heating or cooling drums and rolls continue to rotate even though the seals and bearings may not be functioning as designed.
Conventional rotary joints used with calendar rolls employ a tubular nipple that is mounted upon the end of the calendar roll journal and extends into the housing of the rotary joint. The rotary joint housing is mounted upon the nipple by bearings, such as ball bearings, and sealing structure is located at the end of the nipple associated with a seal supported upon the housing. The outer end of the housing establishes communication with the fluid source, through a head or similar fitting.
With such conventional rotary joints as described above the nipple rotated with the calendar roll journal, and the rotary joint housing is stationary as is the seal mounted on the housing. Of course, the fluid supply fitting or head must be stationary, and with a typical self-supporting rotary joint of this type wherein the majority of the weight of the rotary joint as produced by the housing is stationary and is mounted upon the rotating nipple, radial impact forces imposed upon the roll journal transferred destructive forces upon the nipple and the journal, as well as the joint bearings, often causing serious damage to the seals resulting in a flooding of the joint bearings and eventual bearing failure.
Rotary joints utilizing stationary housings must be relatively large in size, which creates space and clearance problems, and typical rotary joints of the aforedescribed type weigh approximately 190 pounds, which imposes high radial forces on the roll journal structure.
Such conventional rotary joints utilize axially biased annular seals usually formed of sintered carbon, and such seals include an enlarged diameter hub disposed adjacent a smaller diameter seal stem. An O-ring encircling the stem imposes a compressive force thereon, and during roll impact conditions high radial forces may be momentarily imposed upon the seal hub, and the unequal compressive forces imposed upon the seal may cause seal fracture at the junction of the hub and stem seal portions.